Typically, air cooled condensers have been used for cooling or condensing the cooling medium used in a refrigerator. Such air condensers make use of a fan, which consumes current and which is also somewhat noisy. Further, the air condensers often occupy a large space in the boat. In some cases attempts have been made to make use of the sea water outside the boat hull for creating the necessary low temperature for condensing the cooling medium. This often also increases the efficiency, since the sea water is normally substantially colder than the air inside the boat. However, where this is done, exterior cooling slings are mounted unprotected against mechanical actuation from outside, and they are often subjected to corrosion and fouling. This reduces the cooling effect thereof. It is also unsuitable to drill one or more bores through the hull in order to have the exterior condenser tubes or slings extend through the hull, since there may easily appear leakage therefrom. Further, the condenser slings can easily be damaged by objects appearing in the vicinity thereof, since such slings extend completely unprotected along the exterior side of the hull.